DESCRIPTION: The objective of this project is to study the influence of weak DC magnetic fields (0-10 gauss) on several enzymatic reactions that are important in human biochemistry. The heme enzymes nitric oxide synthase, cytochrome P-450, and cytochrome C peroxidase, as well as the B-12 dependent enzyme methionine synthase, are candidates for the site of interaction of 0-10 gauss magnetic fields with biological systems. A magnetic field induced change in the level of nitric oxide, (as produced by nitric oxide synthase), could alter intracellular Ca2+ levels and thereby change Ca2+ efflux rates. This would provide the first causal link between molecular magnetic field effects and a cellular or physiological endpoint of magnetic field exposure. This work could provide a potentially important contribution towards a complete understanding of the possible health effects of environmental magnetic field exposure. The postulated mechanism of interaction is through changes in radical pair recombination, where one radical species is a metal ion (iron in heme, or cobalt in B12).